local-alloc.c (function_invariant_p): New function.

	* local-alloc.c (function_invariant_p): New function.
	(update_equiv_regs): Use function_invariant_p instead of CONSTANT_P
	to decide if an equivalence should be recorded.
	* reload1.c (num_eliminable_invariants): New static variable.
	(reload): Set it.  Use function_invariant_p instead of CONSTANT_P
	to decide if an equivalence should be recorded.
	Unshare PLUS.
	(calculate_needs_all_insns): Skip insns that only set an equivalence.
	Take num_eliminable_invariants into account when deciding
	if register elimination should be done.
	(reload_as_needed): Take num_eliminable_invariants into account
	when deciding if register elimination should be done.
	(eliminate_regs): Handle non-constant reg_equiv_constant.
	* rtl.h (function_invariant_p): Declare.

From-SVN: r24026

4 files changed, 71 insertions, 7 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 74a9a59..ee4b9ff 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,20 @@
+Tue Dec  1 17:58:26 1998  J"orn Rennecke <amylaar@cygnus.co.uk>
+
+	* local-alloc.c (function_invariant_p): New function.
+	(update_equiv_regs): Use function_invariant_p instead of CONSTANT_P
+	to decide if an equivalence should be recorded.
+	* reload1.c (num_eliminable_invariants): New static variable.
+	(reload): Set it.  Use function_invariant_p instead of CONSTANT_P
+	to decide if an equivalence should be recorded.
+	Unshare PLUS.
+	(calculate_needs_all_insns): Skip insns that only set an equivalence.
+	Take num_eliminable_invariants into account when deciding
+	if register elimination should be done.
+	(reload_as_needed): Take num_eliminable_invariants into account
+	when deciding if register elimination should be done.
+	(eliminate_regs): Handle non-constant reg_equiv_constant.
+	* rtl.h (function_invariant_p): Declare.
+
 Mon Nov 30 02:00:08 PST 1998 Jeff Law  (law@cygnus.com)
 
 	* version.c: Bump for snapshot.
diff --git a/gcc/local-alloc.c b/gcc/local-alloc.c
index e8110ac..f112713 100644
--- a/gcc/local-alloc.c
+++ b/gcc/local-alloc.c
@@ -630,6 +630,22 @@ memref_used_between_p (memref, start, end)
   return 0;
 }
 
+/* Return nonzero if the rtx X is invariant over the current function.  */
+int
+function_invariant_p (x)
+     rtx x;
+{
+  if (CONSTANT_P (x))
+    return 1;
+  if (x == frame_pointer_rtx || x == arg_pointer_rtx)
+    return 1;
+  if (GET_CODE (x) == PLUS
+      && (XEXP (x, 0) == frame_pointer_rtx || XEXP (x, 0) == arg_pointer_rtx)
+      && CONSTANT_P (XEXP (x, 1)))
+    return 1;
+  return 0;
+}
+
 /* Find registers that are equivalent to a single value throughout the
    compilation (either because they can be referenced in memory or are set once
    from a single constant).  Lower their priority for a register.
@@ -798,7 +814,7 @@ update_equiv_regs ()
 
       if (REG_N_SETS (regno) != 1
 	  && (! note
-	      || ! CONSTANT_P (XEXP (note, 0))
+	      || ! function_invariant_p (XEXP (note, 0))
 	      || (reg_equiv_replacement[regno]
 		  && ! rtx_equal_p (XEXP (note, 0),
 				    reg_equiv_replacement[regno]))))
@@ -812,7 +828,7 @@ update_equiv_regs ()
 
       /* If this register is known to be equal to a constant, record that
 	 it is always equivalent to the constant.  */
-      if (note && CONSTANT_P (XEXP (note, 0)))
+      if (note && function_invariant_p (XEXP (note, 0)))
 	PUT_MODE (note, (enum machine_mode) REG_EQUIV);
 
       /* If this insn introduces a "constant" register, decrease the priority
diff --git a/gcc/reload1.c b/gcc/reload1.c
index e4dee18..08f5375 100644
--- a/gcc/reload1.c
+++ b/gcc/reload1.c
@@ -338,6 +338,9 @@ int num_not_at_initial_offset;
 
 /* Count the number of registers that we may be able to eliminate.  */
 static int num_eliminable;
+/* And the number of registers that are equivalent to a constant that
+   can be eliminated to frame_pointer / arg_pointer + constant.  */
+static int num_eliminable_invariants;
 
 /* For each label, we record the offset of each elimination.  If we reach
    a label by more than one path and an offset differs, we cannot do the
@@ -659,6 +662,7 @@ reload (first, global, dumpfile)
      Also look for a "constant" NOTE_INSN_SETJMP.  This means that all
      caller-saved registers must be marked live.  */
 
+  num_eliminable_invariants = 0;
   for (insn = first; insn; insn = NEXT_INSN (insn))
     {
       rtx set = single_set (insn);
@@ -674,7 +678,8 @@ reload (first, global, dumpfile)
 	  rtx note = find_reg_note (insn, REG_EQUIV, NULL_RTX);
 	  if (note
 #ifdef LEGITIMATE_PIC_OPERAND_P
-	      && (! CONSTANT_P (XEXP (note, 0)) || ! flag_pic
+	      && (! function_invariant_p (XEXP (note, 0))
+		  || ! flag_pic
 		  || LEGITIMATE_PIC_OPERAND_P (XEXP (note, 0)))
 #endif
 	      )
@@ -692,9 +697,22 @@ reload (first, global, dumpfile)
 
 		      reg_equiv_memory_loc[i] = x;
 		    }
-		  else if (CONSTANT_P (x))
+		  else if (function_invariant_p (x))
 		    {
-		      if (LEGITIMATE_CONSTANT_P (x))
+		      if (GET_CODE (x) == PLUS)
+			{
+			  /* This is PLUS of frame pointer and a constant,
+			     and might be shared.  Unshare it.  */
+			  reg_equiv_constant[i] = copy_rtx (x);
+			  num_eliminable_invariants++;
+			}
+		      else if (x == frame_pointer_rtx
+			       || x == arg_pointer_rtx)
+			{
+			  reg_equiv_constant[i] = x;
+			  num_eliminable_invariants++;
+			}
+		      else if (LEGITIMATE_CONSTANT_P (x))
 			reg_equiv_constant[i] = x;
 		      else
 			reg_equiv_memory_loc[i]
@@ -1335,9 +1353,16 @@ calculate_needs_all_insns (global)
 	  rtx old_notes = REG_NOTES (insn);
 	  int did_elimination = 0;
 	  int operands_changed = 0;
+	  rtx set = single_set (insn);
+
+	  /* Skip insns that only set an equivalence.  */
+	  if (set && GET_CODE (SET_DEST (set)) == REG
+	      && reg_renumber[REGNO (SET_DEST (set))] < 0
+	      && reg_equiv_constant[REGNO (SET_DEST (set))])
+	    continue;
 
 	  /* If needed, eliminate any eliminable registers.  */
-	  if (num_eliminable)
+	  if (num_eliminable || num_eliminable_invariants)
 	    did_elimination = eliminate_regs_in_insn (insn, 0);
 
 	  /* Analyze the instruction.  */
@@ -2698,6 +2723,11 @@ eliminate_regs (x, mem_mode, insn)
 	      }
 
 	}
+      else if (reg_renumber[regno] < 0 && reg_equiv_constant
+	       && reg_equiv_constant[regno]
+	       && ! CONSTANT_P (reg_equiv_constant[regno]))
+	return eliminate_regs (copy_rtx (reg_equiv_constant[regno]),
+			       mem_mode, insn);
       return x;
 
     case PLUS:
@@ -4163,7 +4193,7 @@ reload_as_needed (live_known)
 
 	  /* If we need to do register elimination processing, do so.
 	     This might delete the insn, in which case we are done.  */
-	  if (num_eliminable && chain->need_elim)
+	  if ((num_eliminable || num_eliminable_invariants) && chain->need_elim)
 	    {
 	      eliminate_regs_in_insn (insn, 1);
 	      if (GET_CODE (insn) == NOTE)
diff --git a/gcc/rtl.h b/gcc/rtl.h
index bf9a603..93e7842 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -1440,6 +1440,7 @@ extern void init_optabs			PROTO ((void));
 extern void dump_local_alloc		PROTO ((FILE *));
 #endif
 extern void local_alloc			PROTO ((void));
+extern int function_invariant_p		PROTO ((rtx));
 
 /* In reload1.c */
 extern void reload_cse_regs		PROTO ((rtx));